I have a NAD 7240PE receiver that I am using only for my Niles OS-10 outdoor speakers on my patio. I now would like to install a Niles OS-10SI outdoor speaker on my deck. I want to use this single stereo speaker on the deck, because I only have space for one speaker under my eave. The OS-10 speakers are 8 ohms and the OS-10SI speaker is 4 ohms. The NAD has a 4 or 8 ohm switch on the back. If I would set the the switch on 4 ohms and run both sets at the same time would it harm either or both of the speakers? I have speaker selector setting on the receiver for A,B,and A&B. I would like to be able to have both sets playing at the same time. Thanks for you help.